Unsymmetrical Pentoxy-Substituted Porphyrazines

Abstract

The reactions of 3,6-dipentoxyphthalonitrile (A) in the 1-pentanol3magnesium pentylate medium with phthalonitrile, 2,3-di(methylsulfanyl)-2-butenedinitrile, and 2,3-dihydro-1,4-dithiin-5,6-dicarbonitrile (B) were performed. Unsymmetrically substituted porphyrazines A 3 B were prepared and studied. The influence of the structure of fragment B on the spectral characteristics of the porphyrazines was examined.Much attention is given today to unsymmetrically substituted porphyrazines, which are very promising for various branches of science and engineering [13 4]. The main route to unsymmetrically substituted porphyrazines is random condensation of two o-dinitriles or 1,3-diiminoisoindolines in various molar ratios. The reaction in all cases yields a mixture of all the possible porphyrazines, which are usually separated chromatographically. The product separation is often the most difficulty step; therefore, active efforts are made to develop procedures for selective synthesis of unsymmetrically substituted porphyrazines [537].We reported previously [8] that 3,6-didecyloxyphthalonitrile can be used for selective synthesis of ABAB-type phthalocyanines. 3,6-Dipentoxyphthalonitrile I does not form the corresponding symmetrical octasubstituted phthalocyanine in the reaction with magnesium pentylate in 1-pentanol. At the same time, in the presence of another dinitrile containing no bulky substituents, e.g., 2,3-di(methylsulfanyl)-2-butenodinitrile, a mixture of unsymmetrically substituted porphyrazines is formed.To find the causes of such a behavior of I, it was heated in 1-pentanol in the presence of magnesium pentylate; after removing the solvent, the precipitate was treated with acetic acid and purified by column chromatography (Al 2 O 3 , eluent benzene). We recovered the starting 3,6-dipentoxyphthalonitrile I, as judged from the IR data and comparison of the melting points of I before and after the attempted reaction (cf.[9]). Thus, dinitrile I does not undergo closure of the isoindole ring with the formation of the corresponding alkoxy derivatives. Apparently, for the porphyrazine ring to be formed, the magnesium ion should coordinate four dinitrile molecules. With I, such a coordination is apparently impossible because of steric interactions between bulky substituents in positions 3 and 6. On adding another dinitrile containing no bulky substituents, the formation of fairly stable 1 : 4 complexes becomes possible, and the porphyrazine ring is formed around the metal cation.The absence of octasubstituted phthalocyanines in the reaction products considerably simplifies the chromatographic separation of the product mixture, because the A 3 B products are in all cases the most mobile. The synthesis was performed in accordance with the scheme shown below under the conditions excluding formation of octapentoxyphthaloxyanine.We were able to isolate pure only the compound A 3 B. Chromatographic separation of A 2 B 2 isomers was difficult because of their similar polarity and solubility. Porphyrazines AB 3 were not isolated...

10.1007/s11178-008-2007-6

“…In the electron absorption spectrum of phthalocyanine V (Fig. A similar spectral pattern was previously observed for a phthalocyanine of the A 3 Β type containing three fragments of 3,6-dipentoxyphthalonitrile and one of unsubstituted phthalonitrile [12]. Three-band spectrum in the longwave region is one of the characteristic features of metal-free phthalocyanines of the A 3 Β type, and the most longwave component corresponds to the charge transfer from the donor part of the molecule to the acceptor one [11], whose role play here the fragments of 2-methylbenzimidazole.…”

Unsymmetrical Porphyrazines Based on 3,6-Dioctyloxyphthalonitrile and 5,6-Diphenyl-2,3-dicyanopyrazine and Their Complexes with Copper. Synthesis and Spectral Properties

“…Однако и в этом случае процесс разделения весьма трудоемок. Ранее было показано, [13,14] что использование фталонитрилов, содержащих в положениях 3 и 6 протя-женные алкоксильные заместители позволяет повысить селективность образования несимметричных фталоциа-нинов, поскольку фталоцианины типа А 4 не образуются вследствие стерических затруднений.…”